It's a good idea, yea, but a better idea is letting people create ranks themselves. I was helping a different site with their ranks and I came up with my own design from scratch, the ranks, the colors and everything on my own. They weren't of weapons, instead they we're of characters from the game. Here's a few I made (or mainly, the ones I like the most. Well, those are a few. I made (I think) 30+ different ranks and a total of 200+ images total (due to the bars and such). I also rendered most of the images you see there and also edited them as deemed necessary.
I took the pictures right from in game. It's hard to explain how to render an image. Your best bet is to Google it or look on Good-Tutorials. They have a ton of good tutorials.
I took the rank images and combined the blank space to make 1 blank one and I have all the main weapons by eraser And a few colors. By the way somebody necro'd on the last page.... This is old. To make a weapon just gradient it from the dark shade to the light